Metering pumps are used in a wide variety of industries. Typical uses include the addition of chemicals in liquid form to a reaction vessel or system or even simply for mixing purposes. Metering pumps are also extensively used in the food industry for metering ingredients into processes for the manufacture of processed foods. Other examples of their use will readily come to the mind of those skilled in the art.
Metering pumps also come in various types. One type of particular interest employs a diaphragm which is alternatively employed to draw the fluid to be pumped into a pumping chamber and then discharge the fluid from the pumping chamber. Usually, but not always, the diaphragm is cycled by a pressure fluid such as a pressurized gas or hydraulic fluid under pressure. Of the two, the latter is preferred because the incompressible nature of hydraulic fluid assures that its use as the pressurizing fluid in a diaphragm pump will cause the pump to operate as a positive displacement device throughout its cycle of operation. Consequently, the metering function of the pump is more accurate. Metering pumps today frequently employ pneumatic air cylinders to drive plungers to pressurize fluid to actuate a diaphragm to meter fluids.
Pumps of this sort work well for their intended purpose but systems in which they are employed may be unnecessarily bulky. Moreover, pumps of this type typically have a limited range of capacity. Where adjustment is provided within the range of capacity, the range is not sufficiently great as to encompass the entire spectrum of possible flow rates for which the pump might be used. Consequently, frequently a pump bought for a particular process because of its capability of operating within a capacity range needed for that particular process cannot be used in another materially different process where a completely different capacity range is required.
The present invention is directed to overcoming one or more of the above problems.